LTM4643 datasheet(16/32 Pages) LINER

16 / 32 page

LTM4643

4643fb

For more information www.linear.com/LTM4643

APPLICATIONS INFORMATION

1st Example: Figure 6 for 27°C, or 300K the diode

voltage is 0.598V, thus, 300K = –(1200mV – 598mV)/

–2.0 mV/K)

2nd Example: Figure 6 for 75°C, or 350K the diode

voltage is 0.50V, thus, 350K = –(1200mV – 500mV)/

–2.0mV/K)

Converting the Kelvin scale to Celsius is simply taking the

Kelvin temp and subtracting 273 from it.

A typical forward voltage is given in the electrical charac-

teristics section of the data sheet, and Figure 6 is the plot

of this forward voltage. Measure this forward voltage at

27°C to establish a reference point. Then using the above

expression while measuring the forward voltage over

temperature will provide a general temperature monitor.

Connect a resistor between TEMP and VIN to set the cur-

rent to 100µA. See Figure 31 for an example.

The motivation for providing these thermal coefficients in

found in JESD 51-12 (“Guidelines for Reporting and Using

Electronic Package Thermal Information”).

Many designers may opt to use laboratory equipment

and a test vehicle such as the demo board to predict the

µModule regulator’s thermal performance in their appli-

cation at various electrical and environmental operating

conditions to compliment any FEA activities. Without FEA

software, the thermal resistances reported in the Pin Con-

figuration section are in-and-of themselves not relevant to

providing guidance of thermal performance; instead, the

derating curves provided in this data sheet can be used

in a manner that yields insight and guidance pertaining to

one’s application-usage, and can be adapted to correlate

thermal performance to one’s own application.

The Pin Configuration section typically gives four thermal

coefficients explicitly defined in JESD 51-12; these coef-

ficients are quoted or paraphrased below:

1. θJA, the thermal resistance from junction to ambi-

ent, is the natural convection junction-to-ambient

air thermal resistance measured in a one cubic foot

sealed enclosure. This environment is sometimes

referred to as “still air” although natural convection

causes the air to move. This value is determined with

the part mounted to a JESD 51-9 defined test board,

which does not reflect an actual application or viable

operating condition.

2. θJCbottom, the thermal resistance from junction to the

bottom of the product case, is determined with all of

the component power dissipation flowing through the

bottom of the page. In the typical µModule regulator,

the bulk of the heat flows out the bottom of the pack-

age, but there is always heat flow out into the ambient

environment. As a result, this thermal resistance value

may be useful for comparing packages but the test

conditionsdon’tgenerallymatchtheuser’sapplication.

3. θJCtop, the thermal resistance from junction to top of

the product case, is determined with nearly all of the

component power dissipation flowing through the top

of the package. As the electrical connections of the

typical µModule regulator are on the bottom of the

Figure 6. Diode Voltage VD vs Temperature T(°C)

TEMPERATURE (°C)

–50 –25

0.3

0.5

0.8

0.4

0.7

0.6

100

4643 F06

125

ID = 100µA

Thermal Considerations and Output Current Derating

The thermal resistances reported in the Pin Configura-

tion section of the data sheet are consistent with those

parameters defined by JESD 51-12 and are intended for

use with finite element analysis (FEA) software modeling

tools that leverage the outcome of thermal modeling,

simulation, and correlation to hardware evaluation per-

formed on a µModule package mounted to a hardware

test board: defined by JESD 51-9 (“Test Boards for Area

Array Surface Mount Package Thermal Measurements”).

LTM4643 датащи(PDF) 16 Page - Linear Technology

LTM4643 датащи(HTML) 16 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

датащи скачать

ссылки URL